Rotating systems, including gearboxes and bearings, of wind turbines require lubrication by special lubricants.
Traditionally, an oil pump driven by constant speed supplies an amount of oil to the rotating system to ensure lubrication and cooling of different elements of the rotating system. However, due to the increasing size of modern wind turbines, e.g. having blades of up to 15 tons with a length of up to 60 meters or even larger, a constant supply of oil may result in heavy over-consumption of oil and of energy for driving the pump.